Factors Associated with Adherence to an End-of-Study Biopsy: Lessons from the Prostate Cancer Prevention Trial (SWOG-Coordinated Intergroup Study S9217)

The Prostate Cancer Prevention Trial (PCPT) was a 7-year randomized, double-blind, placebo-controlled trial of the efficacy of finasteride for the prevention of prostate cancer with a primary outcome of histologically determined prevalence of prostate cancer at the end of 7 years. A systematic modeling process using logistic regression identified factors available at year 6 that are associated with end-of-study (EOS) biopsy adherence at year 7, stratified by whether participants were ever prompted for a prostate biopsy by year 6. Final models were evaluated for discrimination. At year 6, 13,590 men were available for analysis. Participants were more likely to have the EOS biopsy if they were adherent to study visit schedules and procedures and/or were in good health (P < 0.01). Participants at larger sites and/or sites that received retention and adherence grants were also more likely to have the EOS biopsy (P < 0.05). Our results show good adherence to study requirements 1 year before the EOS biopsy was associated with greater odds that a participant would comply with the invasive EOS requirement. Monitoring adherence behaviors may identify participants at risk of nonadherence to more demanding study end points. Such information could help frame adherence intervention strategies in future trials.